There are a variety of applications for inspecting the surface cleanliness of manufactured products. A variety of systems have been developed to inspect a multiplicity of surfaces for irregular surfaces as well as contaminants on the surface such as painted panels in the automotive and appliance fields. Some of these surface inspection processes are looking for flaws in the surface or surface finish and also contamination on the surface such as oils or other organic residue. U.S. Pat. No. 4,920,385 is a flaw inspection system that used on sheet materials including aircraft panels for determining surface defects in the panel by reflecting an image of visible light off the irregular surface and thus creating a wavy image in an oppositely positioned camera of the defect. There are numerous other optical methods of measuring the smoothness or contour of a part by imaging a grill or grid of lines on the reflected image of the panel, which become irregular once reflected off an irregular surface.
U.S. Pat. No. 4,863,268 teaches a similar surface detection system to the previous patent for automobile parts for detecting irregularities in the surface of the panel. The source of light and camera are both oriented in the same direction while the reflective surface on the part is used to direct light from the surface being inspected back to the camera. The area of inspection is, of course, very small with only a single light source and a single camera. Such a system would not be particularly useful in inspecting large areas of aluminum aircraft panels of the present invention.
U.S. Pat. No. 5,087,822 teaches another reflection type of inspection system which detects irregularies in the surface of a metal sheet with the use of multiple lamps which reflect visible light sources from different positions off of a sheet being inspected to a single camera. U.S. Pat. No. 5,822,054 detects the presence of defects in the surface of a metal sheet by the same reflective image concept discussed above except by a human inspector. None of the above patents utilize variations in infrared emissivity as a means to detect contamination on the surface nor do any utilize the water break test.